The present invention generally relates to apparatus for mixing, grinding, dispersing and emulsifying liquid mixtures and liquids containing solid particles and, more specifically, to such a device having various improvements generally related to reducing conglomeration of particles, reducing wear and friction related heat problems and increasing productivity.
Many devices employ rotors and stators for wet grinding, mixing, dispersing and emulsifying. In such devices the stator is stationary while the rotor rotates to centrifugally force the liquid to the periphery of the device. During this movement, solid and liquid components of the mixture may be mixed, dispersed, emulsified or ground and finally ejected from the device. Many different grinding or cutting elements of the rotor and stator may be used to reduce the size of solid or semi-solid particulates in the liquid.
One example of a grinding apparatus for reducing the size of solid particulates or particles contained in a liquid is disclosed in U.S. Pat. No. 4,813,617 (the ""617 patent) entitled xe2x80x9cWet Grinding Machine,xe2x80x9d the disclosure of which is hereby fully incorporated by reference herein. This wet grinding machine uses a hollow cylindrical rotor with blades and slots in the wall of the rotor and adjacent rows of slots in the stator. Upper slots in the stator are larger than lower slots such that large particles are disintegrated by, shearing action between the upper stator slots and cooperating rotor slots while smaller particles may be disintegrated by the smaller sized slots in the stator. In most respects the rotor and stator of the ""617 patent have commendable grinding ability, however, the two rows of slots require a longer or deeper rotor and stator. This increases the centrifugal effect and produces a higher vacuum lift of particles into the rotor. Thus, in the above apparatus and other similar apparatus, the rotor and stator may not be able to handle the increased volume of some types of solid particulates caused by the vacuum lifting action. These particulates may then conglomerate in the spiraling fluid and heat up due to friction between the particulates themselves and contact with the rotor and stator. Consequently, the particulates may conglomerate and form a solid or semisolid plug in the rotor. This may, in turn, effectively stop the flow of material through the apparatus and even cause the device to over heat or completely stop operating.
This is a particular problem with polymer particles, such as elastomers used to form adhesives, as these particles tend to soften and stick together at elevated-temperatures. While the liquid may simply travel through the voids between the particles of the conglomerating mass of solid particulates and exit through the slots in the rotor and stator, the solid particulates will gradually stop flowing through the slots in the rotor and stator due to the growing plug or mass of particles.
A device disclosed in U.S. Pat. No. 5,024,647, issued to The United States of America as represented by the United States Department of Energy, uses vanes below a rotor to inhibit formation of vortices within the rotor. However, the device itself is suitable for processing liquids and does not address the conglomeration problem of apparatus for processing liquids and particulates.
Many products processed in rotor/stator devices are slurry solutions that provide good lubrication to bushing or bushings of the device during use. However, in some applications, the product is not an effective lubricant and may even be abrasive. Some products form small spheres and some coagulate and crust as a result of friction induced heat. In the past, devices have employed hardened metal bushings, such as those formed by stellite processes, to overcome the problems of wear and abrasion. This solution, however, is quite expensive and therefore undesirable from a commercial standpoint. Other systems use lubricants to wash abrasives away from bushings, however, it is not often desirable to add a significant amount of lubricating liquid to the product in this manner.
To overcome these and similar problems in this field, it would desirable to provide economically manufactured devices that prevent the conglomeration of particles in centrifugal devices not only to prevent these devices from being completely plugged, but also to prevent any significant fusion of solid particulates that would lead to decreased effectiveness of the device. It would also be desirable to provide grinding devices that work well in abrasive or otherwise harsh applications while maintaining an economic overall design.
It has therefore been one object of this invention to increase the productivity of devices relying on rotor and stators and used for purposes such as mixing, grinding, dispersing or emulsifying liquids containing solid particulates.
It has been another object of this invention to prevent plug formation in a rotor containing liquid and particulates, particularly polymer particulates softenable at elevated temperatures.
It has been yet another object of this invention to improve the circulation of both liquid and particulate solid matter within a rotor and between the rotor and stator of an apparatus for purposes such as grinding, mixing, dispersing or emulsifying.
To these ends, a preferred apparatus of this invention for mixing, grinding, dispersing, emulsifying and the like generally includes a rotatable drive and a rotor body operatively connected to the rotatable drive in any suitable manner. As is typical, the rotor body includes apertures for allowing fluid flow, such as in the form of a slurry solution, into and out of the body. In accordance with the preferred embodiment of the invention, flow divider plate structure extends within the rotor body for preventing conglomeration of particles contained within fluid in the rotor body.
Especially when the present invention is used in connection with grinding and emulsifying operations, a stator body may be attached to support structure of the apparatus and used together with the rotating rotor body to grind or emulsify solid particulates contained within liquid. In this aspect of the invention, the stator body is disposed at least partially within the rotor body and both the stator and rotor bodies include apertures for allowing fluid flow therethrough. These apertures and other blade structures of the apparatus may be designed in accordance with the ""617 patent, for example, or be designed in any other suitable manner. In any case, their function is to shear or otherwise reduce the size of particulate matter preferably as it travels between the respective slots or apertures in the rotor and stator bodies.
Preferably, the flow divider plate structure is stationary relative to the rotor body and is fixed to generally lie along the central axis of the rotor body. For example, the flow divider plate structure may be a single plate that extend at least across substantially the entire diameter of the internal hollow space of the rotor body. The present invention, however, also contemplates flow divider plate structure comprised of two or more flow divider plates lying about the central axis but still extending within the rotor. For example, three or four plates could be extended along and radiate outward from the central axis while generally intersecting at the axis.
The rotor and stator bodies are generally cylindrically shaped in the preferred embodiment and the flow divider plate or plates extend preferably more than halfway into the rotor body from an open end thereof. More preferably, the plate structure extends to a location closely proximate or adjacent a closed end of the rotor body. The flow divider plate or plates are preferably rigidly affixed to support structure of the apparatus, such as the stationary stator body at an open end thereof. In this way, the flow divider plate structure may be maintained stationary relative to the rotor body.
In the preferred embodiment, the drive further includes a drive shaft directly affixed to the rotor body and the apparatus further includes a centering shaft connected between the drive shaft and the flow divider plate or plates. The end of the drive shaft includes a center bushing and the centering shaft is rigidly affixed to the flow divider plate and is disposed within the center bushing such that the drive shaft rotates with respect to the centering shaft. In conjunction with the rigid attachment of the flow divider plate structure to the support structure, such as the stator, the centering shaft therefore ensures that the flow divider plate maintains a stable, central position within the rotor body.
Especially in the cases in which the apparatus is used for grinding or emulsifying solid particulates contained in a liquid, apertures or blade structures in the rotor and stator bodies have shearing edges that cooperate to shear particles contained in liquid conveyed therebetween. Other means of shearing particles within the rotor and stator bodies may also be used, while still realizing benefits from the present invention.
In another aspect of this invention, a lubricant and coolant flushed seal is disposed generally between stationary support structure of the apparatus and the rotatable drive shaft of the apparatus. The seal includes a lip surrounding the rotatable shaft and a source of pressurized liquid is used to flush the lip of the seal with the liquid. The lip seal allows a slow, steady leakage of the pressurized liquid past the seal. This helps prevent abrasive materials from lodging between the drive shaft and the lip of the seal or traveling even farther up into additional mechanical seals or bearings associated with the apparatus. The liquid supplied to the seal may, for example, be water or any other suitable lubricant.
The invention further contemplates a method of grinding, mixing, dispersing or emulsifying a liquid containing solid particulates. Generally, the method comprises the steps of conveying a mixture of liquid and solid particles into a rotating, generally cylindrical rotor body and interrupting a resulting swirling flow of the mixture with a plate extending within the rotor body. This direct interruption of the swirling action prevents conglomeration of particles within the mixture. The flow divider plate structure further aids in this size reduction of the particles and acts as an internal stator.